Water-to-air heat exchangers, or air washers, are apparatus that serve to condition air to a selected lowered or elevated temperature at a desired relative humidity. These apparatus are often used to condition the air in buildings such as textile mills where temperature and relative humidity are important considerations. An example of a system utilized for this purpose is shown in U.S. Pat. No. 3,965,690.
More recently, water-to-air heat exchangers have been used in the postharvest precooling of agricultural produce. In these agricultural applications the produce may be cooled by simply bringing the room containing the produce to a desired temperature and relative humidity. However, the cooling of produce is best achieved, and the freshness of the produce best maintained, by so-called forced air precooling of the produce. In these systems, as generally described in "Commercial Cooling of Fruits and Vegetables", Agricultural Publications, University of California, December, 1972, the air is conditioned to a temperature on the order of 32.degree. F.-36.degree. F. at virtually 100% relative humidity and forced through perforated containers holding produce.
A representative heat exchanger for use in the postharvest forced air precooling of produce is shown at pages 21-22 of the University of California publication referred to above. This heat exchanger takes the form of a vertical chamber which is substantially filled with a packing material. Air to be conditioned is blown upwardly in the chamber in counterflow to water which descends through the chamber. The prior art heat exchangers which have been suggested for use in the mentioned agricultural area are not energy efficient in that the fans required to move the air and the pumps required to move the water consume significantly more energy than is necessary due to, among other things, the substantial back pressure created by the packing material and the substantial quantities of water which must be pumped to achieve the heat transfer, often including recirculation of water through the cooling zone several times.
Thus, it becomes an object of the present invention to provide a heat exchanger that is capable of providing near moisture saturated heated or cooled air in a thermodynamically efficient manner, while reducing the energy required to operate fans and water pumps used to circulate air and water through the heat exchanger.